Reset button, to be able to reset the board easily in case of any misbehaving.

The difference between the input voltage and the output voltage will go in a form of heat. L7805 voltage regulator, so you can plug it to any power source ranged between 7V-12V and the L7805 chip will regulate that voltage and give the ATmega328p chip a well-regulated 5V.DC Power plug to make connecting the board to a power source easy and fast.We added some new components to the bare minimum configuration that we discussed before to add more features to the board and make it more simple to use like a very normal Arduino UNO board. Usually, the ATmega328P chip works on a 16MHz crystal oscillator placed on the pins 9 and 10 but in order to make it oscillate it needs two 22Picofarad capacitors connected to the GND.Д«ut we want to spice things up, let us add some more components to give the board more features and make it more user-friendly. The вЂњResetвЂќ pin is an active low pin, which means if you applied a LOW logic value вЂњ0VвЂќ on it, it will restart the chip. in order to make the ATmega328p runs, you have to apply a HIGH logic value вЂњ5VвЂќ on the вЂњresetвЂќ pin. The ATmega328P works at 5V that must be well regulated without any spikes thatвЂ™s why we are using a 10microfarad capacitor between the 5V power line. but later on, we will add some more components like LEDs, buttons, pin headers.

As you can see, the bare minimum configuration means using the smallest possible quantity of components that makes that thing runs without problems.

Ftdi arduino uno pinout